(1) Field of the Invention
The present invention relates to blowers used on high efficiency (e.g. 90% or higher efficiency) furnaces for drawing air from outside the home into the furnace to support combustion and for expelling the combustion exhaust products outside the home. More particularly, the invention relates to a construction of a blower housing that maximizes the interior space available for the blower impeller.
(2) Description of the Related Art
Combustion blowers for high efficiency furnaces are common in the art. These blowers are used to draw air for combustion from outside the home. Generally, these blowers are located downstream of a combustion chamber or combustion tubes in the furnace, depending upon the style of furnace, into which the combustion air is drawn, mixed with fuel, and ignited to generate heat for the furnace. The exhaust gases are drawn into the suction side of the blower and discharged from the blower through an exhaust pipe that vents to outside atmosphere.
Although the mounting arrangement and available space inside the blower is similar between one furnace model and the next, each model of furnace typically is designed to use a specific type and size blower. Among other general specifications set by the furnace manufacturer, the blower must meet requirements for dimensional size, mounting arrangements, and air moving capacity. In particular, the size of the blower housing must fit within a given space which then in turn determines the location of mounting holes in the furnace bonnet. Thus, these dimensional size requirements limit the air moving capacity of a blower because the impeller size must be chosen to fit and operate efficiently within the given size housing.
In order to increase the air moving capacity of the blower given the fixed size for the blower housing and the impeller, the designer may choose to increase the speed of the impeller. This in turn requires that the blower be operated with a higher speed motor. This option has significant drawbacks, including increased cost to buy, to operate, and increased noise. The speed of the motor and the speed of the impeller must be closely matched to maximize efficiency of the impeller. This requires additional engineering considerations in designing the impeller to operate efficiently at increased speeds. Efficient high speed motors are generally more expensive and tends to increase the cost of the blower. A blower with a higher speed motor also tends to produce more noise and vibration. The higher speed motor also has greater electrical demands. High speed blower motors tend to operate at higher temperatures and generate more heat than lower speed motors. Since the motor is in close proximity to hot exhaust gases in the blower, higher speed motors may require auxiliary cooling systems such as a shaft mounted fan, or a larger bonnet interior to avoid heat buildup. Auxiliary cooling systems lower motor efficiency, and the higher operating temperatures tend to decrease the life cycle of the blower motor.
FIG. 1 shows a blower 20 of the prior art arranged on a blower mounting surface 21 of a furnace 22. The blower 20 includes a blower motor (not shown) and a blower housing 24. In FIG. 1, the blower motor has been removed from its center mount 26 on top of the blower housing 24 to show greater detail of the blower housing 24. The blower housing 24 has a side wall 28 extending between a top piece 30 and a bottom piece 32. The top piece 30 is molded with the center mount recess 26 to receive the blower motor (not shown). The side wall 28, top piece 30, and bottom piece 32 form a volute 34 for the blower housing 24. When the blower 20 is energized, an impeller (not shown), operably connected to a shaft of the blower motor (not shown), rotates in the volute 34 to draw exhaust gases through an inlet hole 35 in the center of the bottom piece 32 and to compress gases in the volute 34. The pressurized exhaust gases are directed into a discharge pipe 36 that extends outward and away from the blower 20 and the furnace 22.
As shown in FIG. 1, mounting feet 38 for attaching the blower 20 to the blower mounting surface 21 of the furnace 22 are provided on the side wall 28 of the blower housing 24. In order to secure the blower housing 24 to the furnace, mechanical fasteners 40 are used. The typical mechanical fastener 40 used to secure the blower 20 to the furnace 22 has a screw head driving end 42 and an opposite driven end 43 spaced from the driving end 42 by a shaft 44. The driving end 42 is larger than the shaft 44 such that it engages a sealing surface 46 on the mounting foot 38 and holds the blower 20 to the furnace. The seating surface 46 of the mounting foot 38 is sized to allow clearance between the driving end 42 of the fastener 40 and the side wall 28 of the blower housing 24.
In the construction of older blower housings, a cut-out in the side wall of the blower housing is sometimes provided adjacent the mounting feet for clearance of the driving end of the mechanical fastener. A sponge foam rubber or rubber type sealing insert is then used once the fastener is installed to completely seal the housing along the narrow spacing adjacent the driving end of the fastener. These inserts and gaskets are problematic in that they tend to leak over time and represent the weak link in exhaust system integrity. Additionally, some blower housing constructions require the use of gasket material to build up the axial height of the bottom piece in the area of the mounting foot when the blower is installed on the furnace. This gasket material seals the blower housing in the area of the mechanical fastener and prevents the mounting foot from heeling over when the mechanical fastener is tightened and the blower housing is attached to the furnace.
What is needed to overcome the disadvantages of the prior art is a blower housing which has a maximized interior space to permit the use of the largest capacity impeller practicable while meeting the size restrictions set by the mounting holes located in the furnace by the manufacturer. The blower housing having the largest practicable capacity impeller would meet the manufacturer's requirements for air moving capacity with a lower speed motor. Such a blower would meet furnace manufacturers' specifications for air moving capacity with decreased noise and vibration, and cost for the blower. Additionally, such a blower would eliminate the need for sealing inserts or gasket materials at the mounting locations for the blower housing.